Model essay.

A healthy 30-year-old woman with blood group Rh negative is found to have rhesus D antibodies at booking at 8 weeks. Critically evaluate the management.

Comment.

This is a basic subject with specialist aspects that you would be expected to know thoroughly.

There is a one page summary in Dewhurst, which gives much of what you need to know and which is worth reading.

There is almost nothing in Luesley and Baker, which is probably a measure of how uncommon the problem has become.

There is a comprehensive review by Wagle & Deshpande on emedicine that gives all you need and more.

For the MCQs, remember that there are more than 40 red cell antibodies that can cause fetal and neonatal haemolysis.

These include c, C, E in the Rhesus system as well as Kell, Duffy, MNS, Lutheran, Kidd etc.
 

Referral to a fetal medicine expert is essential as most obstetricians have no direct experience in managing what has become a relatively uncommon problem. 

Answer.

A check should be made that she has not been given anti-D earlier in the pregnancy.

The woman is not at risk unless she needs a blood transfusion and is wrongly given Rh positive blood.

Or has invasive procedures such as amniocentesis or cordocentesis, which carry slight risks –there has been at least one UK maternal death from peritonitis after amniocentesis.

The Rh negative baby is not at risk.

The Rh positive fetus is at risk of haemolysis: haemolytic disease of the fetus and newborn, HDFN, with potentially serious consequences.

In utero it can become anaemic, develop cardiac failure, hydrops fetalis and die.

As a neonate it can have severe anaemia and hyperbilirubinaemia.

Both can be life-threatening.

Hyperbilirubinaemia can cause kernicterus with brain damage from deposition of bilirubin in the basal ganglia.

This can result in athetosis, cerebral palsy, visual and hearing abnormalities and some loss of cognitive function.

The risk to the Rh positive baby depends on the mother’s history.

The level of antibody should be quantified and expressed in international units, not as a dilution.

The extent to which it increases during the pregnancyis particularly important and must be monitored.

At one extreme the mother may have lost a baby at 24 weeks from hydrops despite having all available care in ideal form.

In this case termination would need to be considered as the prognosis is dire.

At the other, it might be the first affected pregnancy, the antibody level might be low and not increase and the effect on the baby might be minimal.

Without treatment a Rh positive baby will be at least as badly affected as its most-affected sibling.

Unless the baby is Rh negative, the pregnancy must be managed by a fetal medicine specialist with expertise in the condition, as it is now uncommon due to anti-D prophylaxis.

The paediatricians need to be informed and the blood bank given due notice if transfusion is likely.

The father’s genotype can give clues as to the baby’s blood group, but it has to be remembered that up to 5% of “fathers” are not the biological parents, but cuckolds.

If he is Rh negative, the baby will be Rh negative.

If Rh positive and homozygous, the baby will be Rh positive.

If heterozygous, the baby has a 50:50 chance of being positive or negative.

Intermediate groups such as RhD^u need specialist advice as they are weakly positive, but are usually treated as Rh negative.

Cell-free fetal DNA can be obtained from maternal blood and will give the baby’s Rhesus group in most cases.

It is close to, but not 100% accurate, so, if a baby is deemed negative, there should still be some monitoring for rising maternal antibody levels and haemolytic anaemia in late pregnancy to cover possible errors.

Invasive testing with chorionic villus biopsy, amniocentesis and cordocentesis can be used to check the baby’s blood group but carry a risk of miscarriage and further antibody formation.

The only active management is plasmapheresis to reduce antibody levels, but its efficacy is unproven.

Otherwise, management is about detecting fetal anaemia and delivering the baby before it comes to harm or treating it in-utero.

Neonatal treatment will be needed in most cases.

Hyperbilirubinaemia has to be prevented in the neonate.

Maternal antibody levels, particularly high and rising levels indicate high risk.

Doppler studies of middle cerebral artery blood flow can track the onset and progression of anaemia.

They have largely replaced serial amniocenteses with bilirubin assay using optical density difference at 450 nm.

If these are done, the results are plotted on charts derived from Liley to predict the severity of the haemolysis.

Ultrasound scans will also detect evidence of hydrops fetalis in the severely affected baby.

Direct assessment of the anaemia can be done by cordocentesis.

If the haematocrit is low, e.g. < 25 – 30%, transfusion is indicated, depending on gestation to keep the haematocrit at about 45%.

This can be done at cordocentesis and repeated as needed, but cordocentesis can provoke premature delivery.

Cordocentesis has replaced intra-peritoneal infusion of blood.

Blood given to the baby has to be checked against the mother’s serum in case of other antibodies, be screened for infection, like cytomegalovirus, hepatitis and HIV and be gamma irradiated.

Steroids can be given to mature the baby’s lungs in anticipation of early delivery.

Caesarean section may be needed for the very ill baby.

Cord blood should be sent for haemoglobin, blood group, Coomb’s test and bilirubin level.

Exchange transfusion may be needed for the very anaemic baby and establishing i.v. access via the cord may be helpful.

Bilirubin levels must be monitored to prevent kernicterus, which is most likely to happen with the premature baby and those that are ill.

Prediction charts are available describing intervention levels: e.g. bilirubin 350 micromol/l., but less for premature babies.

General supportive measures are feeding, adequate hydration and avoiding cold injury.

Active treatments range from phototherapy with blue light to exchange transfusion.

Hepatic enzyme-inducing drugs like phenobarbitone are no longer used.

Breast feeding is not contraindicated.

The mother needs to be advised of the risks of future pregnancies.

If the prognosis for a Rhesus positive baby is dire, possible treatments should be discussed such as pre-implantation genetic screening if the partner is heterozygous and pregnancy by surrogacy or a Rhesus negative donor if homozygous.

Hand-written without preparation in 22 minutes.

I had to look up the units for bilirubin afterwards.

Word count: 862.

If you can think of any improvements, please let me know.

Remember the usual caveats.

I have tried to cover all the ways the exam committee might mark this essay.

In the exam you will have a template which will enable you to leave out some parts of the essay and concentrate on others.

The template will also tell you how many marks each section of the essay will attract.

I think the template would allow you to eliminate some of the above, making the essay more manageable.

But you could write the above in the time available if you were well-prepared.

Tom McFarlane.